1. Field of the Invention
The invention primarily concerns restorative dentistry, especially methods and devices useful for making out-of-the-mouth or extra-oral dental restorations from dental restorative or composite resin materials. The invention also concerns a model or die from which a prosthetic dental restoration can be made and a method of making such a model or die. The invention further concerns models or dies useful for such purposes as the restoration of art objects such as statues.
2. Description of Related Art
In spite of remarkable technological advances in prosthetic dental restorative or composite resin materials, amalgams typically are easier to install, can be completed in a single visit, and are regarded by many practitioners as having superior durability. For such reasons, the amalgams continue to predominate in posterior dental restorations in spite of their toxicity, aesthetically undesirable color, and the usual need to remove healthy portions of a tooth in order to interlock the amalgam into a cavity. Dental restorative or composite resins also can be applied in a single visit by being tamped into a cavity, shaped or sculptured, then cured by exposure to light and finished with a bur. The step of shaping or sculpturing before curing is cumbersome, as is grinding after curing. Furthermore, shrinkage of the resin during curing produces strain on the tooth and can result in marginal leakage. Even when shrinkage is minimized by incremental curing and the dentist has sufficient skill to sculpture the uncured resin to duplicate the original tooth contour precisely, the procedure is sufficiently demanding and time consuming that the dentist may prefer the convenience of an amalgam. It has been suggested that the effect o resin shrinkage can be minimized by using a model or die to form an extra-oral prosthetic dental restoration such as an inlay. Such a model can be formed from dental or gypsum stone (Plaster of Paris), from thermoplastic resin as in U.S. Pat. No. 2,136,404 (Wheeler), or from epoxy resin as illustrated in Jensen et al., "Polymerization Shrinkage and Microleakage," a paper published in Posterior Composite Resin Dental Restorative Materials edited by Vanherle et al., pages 243-262 (Peter Szulc Publishing Co., The Netherlands, 1985). The Jensen article in a table at page lists advantages and disadvantages of each of in-the-mouth and out-of-the-mouth "`inlay` posterior composites," the advantages of the latter being:
"Reduced stress on cusps from polymerization shrinkage PA1 Better marginal adaptation at gingivo-proximal (no overhang) PA1 Control of proximal contacts PA1 Better contours and anatomy PA1 Easier to obtain a better surface finish PA1 Possible increased abrasion resistance because resin can be heat cured under vacuum" PA1 (1) forming a rubbery, heat-resistant impression of an object to be duplicated (e.g., a tooth, teeth, gingival or gum tissue, or other animate or inanimate object), PA1 (2) filling said impression with a molten thermoplastic resin, PA1 (3) adhering a flexible, dimensionally stable support to said thermoplastic resin and, after the thermoplastic resin solidifies, PA1 (4) removing the thermoplastic resin from said impression to provide a model of said object on said flexible support. PA1 (5) applying restorative resin to a portion of the model where restoration is required (usually after first applying a release agent to the model), PA1 (6) shaping or sculpturing the applied restorative resin to a desired contour, and
Among the listed disadvantages of the out-of-the-mouth or extra-oral "`inlay` posterior composite" are that normally more than one dental appointment is required, thus requiring a temporary restoration, and that there is increased cost due to laboratory procedures.
Although it is easier to gain access to all sides of a dental restoration when working outside the mouth, it can be difficult to shape and polish the interproximal surfaces of a restoration. To that end, individual model teeth are sometimes held in place in a multi-tooth model using flatted pins, or other repositionable locating means. The tooth can then be removed from the model when it is desired to form a restoration, and replaced in the model when it is desired to check interproximal clearance. The pin or other locating means typically must be installed with care, and the first removal of the model tooth usually is performed by sawing through the gingival portion of the model in the interproximal spaces between the tooth.
Of somewhat less relevance to the present invention, but worth noting, is U.S. Pat. No. 626,287 (Modemann) which describes a set of soft rubber teeth attached to a rubber backing strip.